The invention concerns an evaporator intended especially for the sugar industry, with at least two heat exchangers, into the top of which the medium being concentrated is loaded and which are heated with steam with different compositions and/or different pressures in a cross stream, wherein the concentrated medium and the exhaust steam generated is carried away from the heat exchanger separately after it comes out.
These types of heat exchangers are known from EP 0 729 772 A2. Two heat exchangers are arranged one on top of the other in a common cylindrical housing, and they each have their own medium distribution and their own catch basin for the concentrated product. One heat exchanger is heated with hot steam, which comes from a steam turbine, as drawn off steam for example. The exhaust steam generated in the first heat exchanger are then used as a heating medium for the second heat exchanger. The product caught in the catch basin of the top heat exchanger is fed to the medium distributor of the next heat exchanger via a measurement and control device arranged laterally outside the housing.
The problem of the invention is to create an evaporator which is simpler and less expensive in design and with which the heat exchanger can be heated with different steam.
The invention""s solution to this problem is characterized by the fact that the medium being concentrated is loaded by a media distribution common to all heat exchangers, and the medium that left the first heat exchanger goes directly into the next heat exchanger, by the fact that the exhaust steam and the medium are not separated until after the medium comes out of the second heat exchanger and by the fact that the steam spaces in the heat exchanger separated from the exhaust steam space are separated from one another by a common dividing wall.
With the evaporator design in the invention, despite the presence of at least two heat exchangers, only one medium distribution is needed. The medium being concentrated flows through the heat exchanger by gravity and is drawn off out of the bottom part of the evaporator. Each individual heat exchanger can be heated independently with steam despite the formation of one structural unit, so that steam with different compositions and/or different pressures can be used as a heating medium. In particular, it is possible to heat a heat exchanger with polluted or corrosive media, for example with steam that is polluted by corrosive substances in its contents, for example residues from the pulp dryer.
According to another feature of the invention, the condensates from the heat exchangers can be taken out of the heat exchangers through separate pipes, so that it is also possible to separate corrosive and non-corrosive media in this way. If the heat exchanger is heated with corrosive steam, it is possible to make the heat exchanger out of different materials. A heat exchanger heated with corrosive medium is then made of corrosive-resistant material.
One preferred form of embodiment of the invention proposes driving the first heat exchanger with exhaust steam from an evaporator for pulp and the second exchanger with turbine steam from a power plant, for example.